US 3421581 A
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Jan. 14, 1969 J. VAN GEIJN 3,421,581
METHOD AND APPARATUS FOR CARRYING OUT OPERATIONS ON A WELL UNDER WATER Sheet Filed Sept. 12, 1966 F l G.
l NVENTOR JACOB VAN GEIJN BYI H l'S AGENT J. VAN GEIJN Jan. 14, 1969 3,421,581 METHOD AND APPARATUS FOR CARRYING OUT OPERATIONS 7 ON 'A WELL UNDER WATER Z of 2 Sheet File d Sept. 12, 1966 w A 4 a my W 0 7 WE 3 D 4 9 1/ My 2 w LN r I .ll. IJ 5 4 O V 4 4 I A 8 vlllu/ 4 6 11: 7
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INVENTOR H IS AGENT United States Patent 3,421,581 METHOD AND APPARATUS FOR CARRYING OUT OPERATIONS ON A WELL UNDER WATER Jacob Van Geijn, The Hague, Netherlands, assignor to Shell Oil Company, New York, N.Y., a corporation of Delaware Filed Sept. 12, 1966, Ser. No. 578,831
Claims priority, application Great Britain, Oct. 19, 1965,
, 44,242/65 US. (:1. 166.5 9 Claims Int. Cl. E21b 33/035,- E21b 7/12,- E21b 43/01 ABSTRACT OF THE DISCLOSURE Method and apparatus for carrying out operations with respect to an underwater well wherein a pipe string is secured between the well and a platform mounted on a floating vessel over the well site. The platform is mounted for vertical movement relative to the vessel and is continuously biased in an upwardly direction during said relative movement to maintain the drill pipe under tension and compensate for up and down movement of said vessel.
This invention relates to a method and to apparatus for carrying out operations, for example, maintenance work, through a pipe string on an oilor gas well under water.
In deep water, floating structures are sometimes used, from which operations on an oilor gas well are carried out, but difficulty is experienced if the floating structure tends to sway and to move vertically because of waves, since it is rather disturbing when it is necessary to carry out from the structure operations on an oilor gas well under water. It is an object of the invention to provide a method and apparatus having the advantage that the influence of the sway and of the vertical movement of the floating structure is compensated for, so that they no longer disturb the operations to be carried out.
The method according to the invention therefore comprises securing the pipe string to a subsea object such as the wellhead of a well, securing the top part of the pipe string to a platform arranged on a floating vessel which platform is so secured to the vessel that it is movable relatively to the vessel, applying an upwardly directed force to the platform so as to keep the pipe string under tension, and carrying out operations on the well from the platform and through the pipe string.
A floating structure for carrying out the method according to the invention comprises a platform so secured to a floating vessel that it is movable relative to the vessel, a vertical opening in the platform, a clamping device near the opening for securing a vertical pipe string to the platform and means on the structure for applying an upwardly directed force to the platform.
The invention may be carried into practice in various ways but two specific embodiments will not be described by way of example with reference to the drawings in which:
FIGURE 1 is a diagrammatic side elevation of an em bodiment of a floating structure suitable for carrying out the method according to the invention, and
FIGURE 2 shows a modified embodiment of a floating structure suitable for carrying out the method according to the invention.
FIGURES 1 and 2 both show a floating structure 1 floating in a body of water 2 having a water level 3, which structure 1 comprises a vessel 4 and a platform 5. The platform 5 is so secured to the floating vessel 4, for example by suitable vertical guide means (not shown), that it is vertically movable relatively to the vessel 4. A vertical opening 6 is present in the platform 5. Adjacent to Patented Jan. 14, 1969 the opening 6 is arranged a clamping device 7 which serves for securing a vertical pipe string 8 to the platform 5. In the vessel 4 a vertical hole 9, which is for example cylindrical, is present to allow the pipe string 8 to pass through the vessel 4. Emergency controls must be provided to stop the platform 5 from shooting upwardly in the event of the pipe string 8 breaking or becoming loosened. Before the pipe string 8 is connected to a wellhead it must be possible to raise and lower the platform 5 and only when the pipe string 8 has been connected to the wellhead will the platform 5 be allowed to exert an upward force on the pipe string 8.
The clamping device 7 is preferably removable, and can also be used to raise or lower pull out pipe strings between the structure and the wellhead. The vertical hole 9 should be large enough to permit lifting through hole 9 of Christmas trees, blow-out preventers or other equipment. Furthermore, the hole 9 need not be cylindrical, but it may widen from its upper to its lower ends.
In the embodiment shown in FIGURE 1 cables 10 are secured to the platform 5, the other end of each cable 10 being provided with a weight 11 and each cable 10 being led over a pllley 12. Each pulley 12 is rotatably secured to a piller 13 which is supported by the vessel 4. Each pulley 12 is arranged at a level above the highest possible position of the platform 5 relative to the vessel 4.
The floating structure as shown in FIGURE 1 is used as follows.
One end of at least one pipe string 8 is latched on to a subsea object, for example to an oil well (not shown), for example by using divers, or guiding cables, or a remotely operated propulsion device having a television camera. The pipe string 8 is connected with one end to the subsea object by suitable connections, for example by connections which can be remotely operated and which may include emergency releases. The upper end of the pipe string 8 is passed through the hole 9 and through the opening 6. By means of the clamping device 7 the upper end of the pipe string 8 is fixedly secured to the platform 5. The weights 11 secured by the cables 10 to the platform 5 exert upwardly directed forces on the platform 5 and since the platform 5 is secured to the end of the pipe string 8, the latter will always be kept under tension. If the vessel 4 moves vertically because of the waves, the platform 5 will remain in its position so that the vessel 4 will move vertically relatively to the platform 5. When the vessel 4 moves upwardly the pillars 13 and the pulleys 12 will move upwardly as well and since the platform 5 remains stationary the pulleys 12 will be caused to rotate and the weights 11 will be displaced upwardly relatively to the platform 5. When the vessel 4 moves downwardly the platform 5 will remain stationary and the pulleys 12 will be caused to rotate in the opposite direction and the weights 11 will be displaced downwardly relatively to the platform 5. From the above, it will be clear that, irrespective of the waves, the platform 5 will always remain at the same level and that the pipe string 8 will always be kept under tension.
From the platform 5 drillingor wireline operations can be carried out. The platform 5 can be provided with conventional equipment for carrying out wireline operations, for example equipment as shown in FIGURE 1 and indicated by the numbers 14, 15, 16, 17, 18, 19, 20, 21, 22. Since this equipment does not form part of the invention it will not be discussed in detail.
The embodiment as shown in FIGURE 2 is provided with a hydraulic system for moving the platform 5 relatively to the vessel 4 instead of the system comprising weights 11 as shown in FIGURE 1. It is remarked, however, that instead of counterweights or a hydraulic system it is also possible to use a pneumatic or an electrical system, if desired. On the vessel 4 a number of (for example four) hydraulic cylinders 23 is arrange din each of which a plunger or piston (not shown) is present which is axially movable in the cylinder 23. To each plunger or piston a bar or rod 24 is secured, of which the upper end is connected to the platform 5. The connection of the bars or rods 24 with the platform may be direct or through a gimbal support. The axial (vertical) movement of the bars or rods 24 may be controlled by any suitable control system which senses the deviation or any derivative of the deviation of the platform from the desired horizontal plane. In the system as shown in FIGURE 2, the deviation of the platform from the desired horizontal plane is sensed by a sensing device 25. From the sensing device 25 signals can be transmitted through a line 26 to a controller 27. The tension in the pipe string 8 can be sensed by sensing devices 28 which are each connected to one of the cylinders 23 by lines 29. Each sensing device 28 is connected to the controller 27 by lines 30 through which signals can be transmitted from the sensing devices 28 to the controller 27. The controller 27 can process the signals, received from the sensing devices 25 and 28, and can decide on the hydraulic pressures required in the cylinders 23 to keep the platform 5 in the desired horizontal plane and to keep the pipe string 8 under the proper tension. The controller 27 can then regulate the pressure in the cylinders 23 accordingly, e.g. by operating threeway control valves 31 and 32 by sending through lines 35 signals to servo-valve mechanisms 33 and 34. The valves 31 and 32 are arranged respectively in a line 36 and in a line 37 which each connect the pressure side of a liquid-pump 38 with a corresponding cylinder 23. The suction side of the pump 38 is connected through a line 39 to a tank 40 containing a suitable liquid, for example oil. A drain line 41 connects the valve 31 with the top of the tank 40 and a drain line 42 connects the valve 32 to the drain line 41. By properly positioning the threeway valves 31 and 32, liquid can be pumped from the tank 40 to the cylinder 23 and/or be drained from the cylinders 23 so that the proper pressure will be obtained in each of the cylinders 23. By means of the hydraulic system as described above the platform 5 will, irrespective of the waves, always remain in the desired horizontal plane and the pipe string 8 will always be kept under tension.
On the platform 5 can be located conventional equipment for carrying out drilling operations, for example a derrick 43, a hoist 44, a cable 45, a travelling block 46 (shown in FIGURE 2) for lowering the pipe string 8 or hoisting the pipe string 8 from the hole 9 or for lowering pipes 48 into or hoisting pipes 48 from the pipe string 8.
It is to be noted that instead of the counterweights or the hydraulic system as described it is possible to use a pneumatic or electric system. It is for example possible to keep the pressure in each cylinder 23 substantially constant in all positions of the platform 5 by connecting each cylinder 23 to a corresponding pressure tank (not shown), containing gas and having a volume which is large relative to the volume of the corresponding cylinder 23.
Furthermore attention is drawn to the fact that instead of one pipe string 8 as shown, it is possible to use a plurality of pipe strings which are parallelly or concentrically arranged.
I claim as my invention:
1. A method of carrying out operations, for example maintenance work, on a well under water through a pipe string, comprising securing the pipe string to a subsea wellhead of a well, securing the top part of the pipe string to a platform, arranging said platform on a floating vessel in a manner such that the platform is vertically movable relatively to the vessel, applying an upwardly directed force to the platform with said force independent of the motion of said vessel so as to keep the pipe string under tension, and carrying out operations on the Well from the platform and through the pipe string.
2. The method as claimed in claim 1, wherein the upward force acting on the platform is created by means of a weight.
3. The method as claimed in claim 1, in which the upward force acting on the platform is created by a piston arranged in a fluid cylinder.
4. A floating structure for carrying out operations at offshore locations, said structure comprising a platform so secured to a floating vessel that it is vertically movable relatively to the vessel, a vertical opening in the platform, a clamping device near the opening for securing a vertical pipe string to the platform and means on the structure for applying an upwardly directed force to the platform as said platform moves vertically relative to said vessel.
5. The structure as claimed in claim 4, in which the means for applying an upwardly directed force to the platform comprise a cable having one end secured to the platform and the other end to a weight, the cable being led over a pulley which is arranged on the structure at a level above the highest position of the platform relatively to the vessel.
6. The structure as claimed in claim 4, in which the means for applying an upwardly directed force to the platform comprise a cylinder arranged on the structure, a piston arranged in the cylinder, a connection between the piston and the platform, and fluid under pressure in the cylinder.
7. The structure as claimed in claim 6, in which means are present for controlling the pressure in the cylinder.
8. The structure as claimed in claim 6, in which a system is present for keeping the pressure in the cylinder substantially constant in all positions of the platform relatively to the vessel.
9. The structure as claimed in claim 8, in which the system for keeping the pressure in the cylinder constant comprises a pressure tank containing gas and having a volume which is large relative to the volume of the cylinder, and a fluid connection between the cylinder and the pressure tank.
References Cited UNITED STATES PATENTS 2,181,641 11/1939 Hicks -220 X 3,110,350 11/1963 Spiri 1755 3,177,954 4/1965 Rand 166.6 X 3,179,179 4/1965 Kofahl 166.5 3,195,639 7/1965 Pollard et a1 1757 X 3,221,817 12/1965 De Vries et a1. 166.5
CHARLES E. OCONNELL, Primary Examiner.
R. E. FAVREAU, Assistant Examiner.
US. Cl. X.R. 1755, 27